1. Field of Invention
The present invention is directed to retractable ball seats for use in oil and gas wells and, in particular, to retractable ball seats having time delay materials for releasing the ball.
2. Description of Art
Retractable ball seats are generally known in the art. For example, U.S. Pat. No. 3,211,232 discloses a typical retractable ball seat having a collet, a passageway through the collet, and a ball or drop plug. The ball or drop plug is disposed on the seat, preventing fluid from flowing through the passageway. As the fluid pressure above the ball or drop plug builds up, the fluid pressure actuates a tool connected to the retractable ball seat. Thereafter, the collet is moved from its retracted position to its expanded position and the ball or drop plug falls through the passageway. As a result, fluid is no longer being blocked by the retractable ball seat.
Although modifications of retractable ball seats have been made, such as those disclosed in U.S. Pat. No. 4,390,065 and U.S. Patent Application Publication No. 2005/0205264, the prior art utilized shear pins or other pressure building methods that caused the ball seat to release the ball only when a certain downhole pressure was reached. However, in some instances sufficient pressure may not be available. Alternatively, in some wells, pressure, even if available, cannot be utilized because additional intervention steps are required which results in the well experiencing undesirable “downtime” for the additional intervention steps. Additionally, in some instances, the shear pins fail to shear when they are supposed to, causing further delays.
Accordingly, prior to the development of the retractable ball and plug seats disclosed herein, the art has sought retractable ball and plug seats that can be activated to actuate downhole tools where pressure is unavailable to set the downhole tools and that can be activated after a known elapsed period of time.